MoOPH Transition State on:
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MoOPH, also known as oxodiperoxymolybdenum(pyridine)-(hexamethylphosphoric triamide), is a
Due to MoOPH's 
In addition, 
In the case of sulfones, alpha-hydroxylation leads directly to the ketone or aldehyde.
Common byproducts of the alpha-hydroxylation tend to include overoxidation to the corresponding dicarbonyl or intermolecular aldol reaction of the starting material. Procedures to prevent side reactions include the inverse addition of the enolate to MoOPH or careful control of the temperature (-78 to -20 °C). Notable miscellaneous reactions include MoOPH’s ability to oxidize alkylboranes directly to the alcohol with net stereo-retention.
MoOPH has also been shown to oxidize N-trimethylsilyl amides directly to the hydroxamic acid.
reagent
In chemistry, a reagent ( ) or analytical reagent is a substance or compound added to a system to cause a chemical reaction, or test if one occurs. The terms ''reactant'' and ''reagent'' are often used interchangeably, but reactant specifies a ...
used in organic synthesis
Organic synthesis is a branch of chemical synthesis concerned with the construction of organic compounds. Organic compounds are molecules consisting of combinations of covalently-linked hydrogen, carbon, oxygen, and nitrogen atoms. Within the gen ...
. It contains a molybdenum
Molybdenum is a chemical element; it has Symbol (chemistry), symbol Mo (from Neo-Latin ''molybdaenum'') and atomic number 42. The name derived from Ancient Greek ', meaning lead, since its ores were confused with lead ores. Molybdenum minerals hav ...
(VI) center with multiple oxygen ligands, coordinated with pyridine
Pyridine is a basic (chemistry), basic heterocyclic compound, heterocyclic organic compound with the chemical formula . It is structurally related to benzene, with one methine group replaced by a nitrogen atom . It is a highly flammable, weak ...
and HMPA
Hexamethylphosphoramide, often abbreviated HMPA, is a phosphoramide (an amide of phosphoric acid) with the formula This colorless liquid is used as a solvent in organic synthesis.
Structure and reactivity
HMPA is the oxide of tris(dimethylamino ...
ligands, although the HMPA can be replaced by DMPU
''N'',''N''′-Dimethylpropyleneurea (DMPU) is a cyclic urea sometimes used as a polar, aprotic organic solvent. Along with the dimethylethyleneurea, it was introduced as an analog of tetramethylurea.
In 1985, Dieter Seebach showed that it is ...
. It is an electrophilic
In chemistry, an electrophile is a chemical species that forms bonds with nucleophiles by accepting an electron pair. Because electrophiles accept electrons, they are Lewis acids. Most electrophiles are positively charged, have an atom that carr ...
source of oxygen that reacts with enolate
In organic chemistry, enolates are organic anions derived from the deprotonation of carbonyl () compounds. Rarely isolated, they are widely used as reagents in the Organic synthesis, synthesis of organic compounds.
Bonding and structure
Enolate ...
s and related structures, and thus can be used for alpha-hydroxylation
In chemistry, hydroxylation refers to the installation of a hydroxyl group () into an organic compound. Hydroxylations generate alcohols and phenols, which are very common functional groups. Hydroxylation confers some degree of water-solubility ...
of carbonyl
In organic chemistry, a carbonyl group is a functional group with the formula , composed of a carbon atom double bond, double-bonded to an oxygen atom, and it is divalent at the C atom. It is common to several classes of organic compounds (such a ...
-containing compounds. Other reagents used for alpha-hydroxylation via enol or enolate structures include Davis oxaziridine, oxygen
Oxygen is a chemical element; it has chemical symbol, symbol O and atomic number 8. It is a member of the chalcogen group (periodic table), group in the periodic table, a highly reactivity (chemistry), reactive nonmetal (chemistry), non ...
, and various peroxyacid
A peroxy acid (often spelled as one word, peroxyacid, and sometimes called peracid) is an acid which contains an acidic group. The two main classes are those derived from conventional mineral acids, especially sulfuric acid, and the peroxy deri ...
s (see Rubottom oxidation
The Rubottom oxidation is a useful, high-yielding chemical reaction between silyl enol ethers and peroxyacids to give the corresponding acyloin, α-hydroxy carbonyl product.Kürti, pp. 388–389.
). This reagent was first utilized by Edwin Vedejs
Edwin Vedejs () (; January 31, 1941 – December 2, 2017) was a Latvian-American professor of chemistry. In 1967, he joined the organic chemistry faculty at University of Wisconsin. He rose through the ranks during his 32 years at Wisconsin being ...
as an efficient alpha-hydroxylating agent in 1974 and an effective preparative procedure was later published in 1978.
Synthesis
MoOPH is synthesized frommolybdenum trioxide
Molybdenum trioxide describes a family of inorganic compounds with the formula MoO3(H2O)n where n = 0, 1, 2. The anhydrous compound is produced on the largest scale of any molybdenum compound since it is the main intermediate produced when molybd ...
by oxidation with hydrogen peroxide
Hydrogen peroxide is a chemical compound with the formula . In its pure form, it is a very pale blue liquid that is slightly more viscosity, viscous than Properties of water, water. It is used as an oxidizer, bleaching agent, and antiseptic, usua ...
and addition of the HMPA
Hexamethylphosphoramide, often abbreviated HMPA, is a phosphoramide (an amide of phosphoric acid) with the formula This colorless liquid is used as a solvent in organic synthesis.
Structure and reactivity
HMPA is the oxide of tris(dimethylamino ...
and pyridine
Pyridine is a basic (chemistry), basic heterocyclic compound, heterocyclic organic compound with the chemical formula . It is structurally related to benzene, with one methine group replaced by a nitrogen atom . It is a highly flammable, weak ...
ligands:
Reactivity
Due to MoOPH's steric bulk
Steric effects arise from the spatial arrangement of atoms. When atoms come close together there is generally a rise in the energy of the molecule. Steric effects are nonbonding interactions that influence the shape ( conformation) and reactivi ...
, preferential attack at the O–O bond occurs from the less hindered enolate face in the absence of stereoelectronic factors.
In addition, nitrile
In organic chemistry, a nitrile is any organic compound that has a functional group. The name of the compound is composed of a base, which includes the carbon of the , suffixed with "nitrile", so for example is called " propionitrile" (or pr ...
s with acidic alpha protons can be converted directly to cyanohydrin
In organic chemistry, a cyanohydrin or hydroxynitrile is a functional group found in organic compounds in which a cyano and a hydroxy group are attached to the same carbon atom. The general formula is , where R is H, alkyl, or aryl. Cyanohyd ...
s; however, in the case of branched nitriles, this reaction directly affords the ketone.
In the case of sulfones, alpha-hydroxylation leads directly to the ketone or aldehyde.
Common byproducts of the alpha-hydroxylation tend to include overoxidation to the corresponding dicarbonyl or intermolecular aldol reaction of the starting material. Procedures to prevent side reactions include the inverse addition of the enolate to MoOPH or careful control of the temperature (-78 to -20 °C). Notable miscellaneous reactions include MoOPH’s ability to oxidize alkylboranes directly to the alcohol with net stereo-retention.
MoOPH has also been shown to oxidize N-trimethylsilyl amides directly to the hydroxamic acid.
References
{{reflist Reagents for organic chemistry Molybdenum(VI) compounds Pyridine complexes Phosphoramides Peroxides